Optimization of annealing conditions of (GaIn)(NAs) for solar cell applications

(GaIn)(NAs) lattice matched to GaAs and Ge and having a 1 eV bandgap is a promising candidate for future space and terrestrial multi-junction solar cell structures. The present paper summarizes results of a detailed annealing study of the metastable quaternary alloy having an In content of 8% and a N content of 2.8%. It is shown that photoluminescence (PL) intensity can be taken as a measure of improving minority carrier characteristics in solar cell devices. A direct correlation between PL intensity and quantum efficiency in the (GaIn)(NAs) material system is observed. The annealing conditions, e.g. anneal temperature, time and As-stabilization, have to be adapted to the particular In content of the material in order to initiate the site change of the nitrogen atom from a Ga-rich environment upon growth to an In-rich one after annealing. In addition, the dissolution of chain-like N-ordering in [0 0 1] direction is detected. The greatly enhanced optical performance leads to an improved quantum efficiencies of the (GaIn)(NAs) solar cell material.